Cellular communication systems are known. In such systems, a subscriber or user, purchases a mobile communication unit which provides the user with access to the cellular communication system. When the user purchases the mobile communication unit, the mobile communication unit is assigned a mobile identification number (MIN) and electronic serial number (ESN) which are used to identify the mobile communication unit when it operates within the cellular communication system, and therefore, identifies the user for billing purposes. When in use, the mobile communication units communicate, via radio transmission, with base station transceivers within the cellular communication system. The base station transceivers further communicate with a base station controller which in turn communicates with a mobile switching center (MSC). From the MSC, a user can be connected to other cellular communication system users or to public switch telephone network (PSTN) users. In establishing communications within the cellular system, the mobile communication unit is required to broadcast, over the air, the MIN and the ESN. This is required so that the mobile switching center serving the cellular communication system can identify the mobile communication unit operating in the cellular communication system so that calls placed or received by the mobile communication unit may be properly identified and billed.
Cellular pirates, fraudulent users of the cellular communication system, have developed methods of intercepting the MIN and ESN numbers during such broadcasts when the mobile communication unit is operating in the cellular communication system. The cellular pirates have also developed methods of programming "clone" mobile communication units with the intercepted MIN and ESN numbers. When a clone mobile communication unit accesses the system, the cellular system recognizes the MIN and ESN as being valid and allows the call to proceed. The call, however, is billed to the legitimate cellular user whose mobile communication unit was programmed with the intercepted MIN and ESN. Ultimately, the cellular system operator absorbs losses due to fraudulent calls by not collecting for the fraudulent calls and from lack of system use by legitimate users who have lost confidence in the system.
As a result of such cellular communication system fraud, cellular system operators are subject to extensive losses of revenue. In response, methods to combat the fraudulent use of mobile identification numbers have been developed. For example, it is known to scramble or otherwise encrypt the MIN and ESN during broadcast. This makes intercepting a MIN substantially more difficult. The MIN may still be intercepted, however, and once a MIN is intercepted, it can be used to fraudulently access the cellular communication system.
Another system monitors the cellular communication system for simultaneous use of a MIN. If the same MIN appears registering with the system, i.e., more than one cellular phone attempting to seek access to the system using the same MIN, the system recognizes a fraud situation and locks out the MIN from further use of the cellular system. The legitimate user must then contact the cellular operator to receive a new MIN before being allowed further use of the cellular system, and the fraudulent user is locked out. This method suffers several disadvantages. For example, fraudulent users are only detected if there is simultaneous access to the system. Therefore, unless the legitimate user, or a second fraudulent user, are registering within the cellular communication system at the same time as the pirate user, no fraud is detected. Therefore, MINs are still intercepted and used until a fraudulent use is detected. At that time, the legitimate user, at an extreme inconvenience, is forced to contact his cellular operator for a new MIN and is unable to use the cellular system until they do so.
Another system for detecting fraud monitors the radio frequency signatures, or fingerprints, of mobile communication units to identify legitimate users and deny access to the system by fraudulent users. This system, however, requires the cellular system operator to purchase and maintain additional hardware and software. In addition, there is additional processing involved for each call placed, increasing power consumption within the cellular communication equipment and increasing the connection time for the user placing or receiving a call. Therefore, while each of these systems help prevent cellular fraud, there remains a need for further enhancing the security of the cellular system.